docs: def _cleanup_old_backups(self, database=None, servername=None):
          """
          Cleanup old backups, keeping the number of backups specified by
          DBBACKUP_CLEANUP_KEEP and any backups that occur on first of the month.
          """
          self.storage.clean_old_backups(encrypted=self.encrypt,
                                         compressed=self.compress,
                                         content_type=self.content_type,
                                         database=database,
                                         servername=servername)